A number of different numerical rankings for journals exist. This section contains information on several different numerical methods used to measure a journal's importance. Additional information on metrics is available in Science Metrics, Nature Special Issue, June 16, 2010.
A number of different journal ranking measures exist. They are described in the following boxes:
The Thomson-Reuters (formerly ISI) Impact Factor is the oldest quantitative measure of journal prestige. It is calculated based on the number of citations during a given year to journal articles published in the previous two years. There are some concerns about using the Impact Factor to judge research, because it varies by discipline and type of article (for example, review articles are usually cited more than research articles). See the article by Seglen linked below. In addition, an article that is scientifically inaccurate could be cited by other articles that are critical of the methods and techniques used in the inaccurate article.
NOTE OF CAUTION: Some disreputable publishers may claim that they have an Impact Factor. The Impact Factor that matters most is the one reported by Thomson-Reuters in Journal Citation Reports (JCR), which is based on titles that are indexed in Science Citation Index and Social Science Citation Index. WIU does not provide access to JCR, but it is possible to check the title lists for Science Citation Index and Social Science Citation Index to see if the journal is indexed. If it is not, then the claimed "Impact Factor" is probably not valid.